CN101666625B - Model-free method for correcting distortion error - Google Patents

Abstract

A model-free method for correcting distortion error belongs to the technical field of computer image identification. In the prior art, the mathematic model is established, the correction method is complex and the measurement precision depends on the established mathematic model; furthermore, the established mathematic models have similarity and are different from the practical situation, thus causing that the improvement of the measurement precision is restricted. In the invention, the mesh of any two imaged points of the object to be measured in a mesh plate distorted after imaging is determined firstly, thus obtaining the coordinates of the two points in the mesh plate coordinate system and working out the image dimensions between the two points; secondly, coordinate systems are established respectively in the mesh in which the two points are arranged, thus working out the image dimensions between the two points and the respective origins of the two coordinate system; and thirdly, the three image dimensions obtained in the previous two steps are added so as to obtain the image dimensions between any two points of the object to be measured. In the invention, the distorted mesh plate is directly used for measuring the distances of the two points on the object to be measured in the mesh plate coordinate system. When the dimension precision of the mesh plate is 0.2 microns, the measurement precision is higher than 3 microns.

Description

Model-free method for correcting distortion error

Technical field

The present invention relates to a kind of model-free method for correcting distortion error; In adopting computer image processing technology measure two dimensional target surface dimension process; Correction belongs to the computer image recognition technology field because of the distortion error that measurement mechanism optical parallax, machine error, electricity error are caused.

Background technology

Active computer Flame Image Process two dimension target surface dimension measurement method is unit representation picture size with the pixel, and there is conversion relation in object under test physical size just target surface size and its picture size.In order to find out target surface size and the picture size conversion relation between the two, the measure of being taked is to adopt the known standard footage number fixed, and so-called gauge is exactly a kind of two-dimentional chi, and waffle slab then is a kind of two-dimentional chi commonly used.Earlier waffle slab is placed the target surface position, lighting condition is identical with actual measurement, obtains the waffle slab image.If the target surface between the known waffle slab any two adjacent cross centers is of a size of d, to see shown in Figure 1ly, respective pixel in the waffle slab image (pixel) number is n, then tries to achieve calibration coefficient k=d/n.Any 2 p on the waffle slab ₁, p ₂Picture size n between the corresponding point on the waffle slab image _LObtain through Computer Image Processing, then any 2 p on the waffle slab ₁, p ₂Between target surface size L be:

L＝kn _L (1)

Object under test is replaced waffle slab, can obtain object under test target surface size through contrast.

Yet, in target surface dimensional measurement process, uneven because of lens distortion and pixel size, arrange reasons such as irregular; Cause pattern distortion; See shown in Figure 2, thereby the distortion error that the picture size of make measuring exists, the precision of the target surface size that obtains therefrom is affected.This just needs to improve target surface dimensional measurement precision through the correcting distorted in other words error of correcting image distortion.For same measurement mechanism, its pattern distortion is constant.No matter waffle slab image or object under test image, its pattern distortion is identical.So existing distortion error bearing calibration is:

1, measures each cross center distortion error on the waffle slab image of waffle slab

This process is also referred to as demarcation.On waffle slab, setting up the waffle slab coordinate system is o-xy, sees shown in Figure 1ly, and the coordinate of any cross of waffle slab center p in o-xy is p (x _i, y _j) i is that cross center p is listed as in the waffle slab coordinate system number, j is cross center p row number in the waffle slab coordinate system, because the target surface size d at any two the adjacent cross centers of waffle slab is known, and p (x then _i, y _j) value representation in o-xy is:

$\left\{\begin{array}{c}{x}_i=i\×d\\ y_j=j\×d\end{array}\right.(i=\mathrm{0,1},...,N;j=\mathrm{0,1},...,M)---\left(2\right)$

If image coordinate system is o '-x ' y ', see shown in Figure 2ly, move to o-xy among o '-x ' y '.If the coordinate of o-xy initial point O in o '-x ' y ' is o (x after the translation ₀, y _o), the cross center coordinate of p in o '-x ' y ' is:

$\left\{\begin{array}{c}{x_i}^{\′}=i\×d+x_0\\ {y_j}^{\′}=j\×d+y_0\end{array}\right.(i=\mathrm{0,1},...,N;j=\mathrm{0,1},...,M)---\left(3\right)$

But because pattern distortion takes place, the cross center actual coordinate of p in o '-x ' y ' is (X _i, Y _j), then the distortion error of cross center p in the waffle slab image is:

$\left\{\begin{array}{c}\mathrm{\Δ}{x}_i=X_i-i\×d-x_0\\ \mathrm{\Δ}{y}_j=Y_j-j\×d-y_0\end{array}\right.(i=\mathrm{0,1},...,N;j=\mathrm{0,1},...,M)---\left(4\right)$

2, set up mathematical model and proofread and correct the object under test distortion error

After first step acquisition waffle slab distortion in images error, set up mathematical model and proofread and correct the object under test distortion error.Like method between dividing regions is that the waffle slab image is divided into several bigger rectangular areas according to the distortion error distribution situation, and as 3 * 3, this process is modeling, sees shown in Figure 3ly, is the selected normal value correcting value (dx in each rectangular area _i, dy _i); Should obtain by formula (4) by normal value correcting value; Judge then and a bit drop on which rectangular area on the object under test, just get the corrected value of the normal value correcting value of this rectangular area, proofread and correct its coordinate in image coordinate system o '-x ' y ' of back and be as these corresponding point on the object under test image:

$\left\{\begin{array}{c}{X_i}^{\′}=X_i-d{x}_i\\ {Y_j}^{\′}=Y_j-d{y}_i\end{array}\right.---\left(5\right)$

Multiply by calibration coefficient k again, obtain that coordinate is in waffle slab coordinate system o-xy:

$\left\{\begin{array}{c}{x}_i=k{X_i}^{\′}\\ y_j=k{Y_j}^{\′}\end{array}\right.---\left(6\right)$

Adopt said method, obtain any 2 A on the object under test respectively ₁, A ₂Coordinate after in waffle slab coordinate system o-xy, proofreading and correct

With

According to the distance between two points formula, try to achieve A ₁, A ₂2 target surface size L _AFor:

$L_A=\sqrt{{(x_{A_1}-x_{A_2})}^2+{(y_{A_1}-y_{A_2})}^2}---\left(7\right)$

In addition; Existing method of proofreading and correct the object under test distortion error also has method of interpolation, fitting process etc., sees the Xian Inst. of Optics and Precision Mechanics, Chinese Academy of Sciences's PhD dissertation that is entitled as " research of high speed optoelectronic transit photographic film image information processing technology " that Deng Nianmao calendar year 2001 delivers for details.

Prior art is set up mathematical model makes bearing calibration loaded down with trivial details, and measuring accuracy relies on the mathematical model of being set up, and the mathematical model of being set up all has approximation, there are differences with actual conditions, causes the raising of measuring accuracy to be restricted.

Summary of the invention

In order to eliminate prior art because of realizing that through setting up mathematical model distortion error proofreaies and correct the restriction that the raising to measuring accuracy brings, we have invented a kind of model-free method for correcting distortion error.

The present invention's model-free method for correcting distortion error is characterized in that; At first; Residing grid in the waffle slab of confirming after imaging, to take place to distort after any 2 imagings of object under test; Thereby obtain this 2 coordinates in the waffle slab coordinate system, obtain the target surface size between these 2 residing grids; Secondly, in said 2 residing grids, set up coordinate system respectively, obtain and the target surface size between coordinate origin separately at these 2; The 3rd, the addition of preceding two resulting three target surface sizes of step is obtained the target surface size of any point-to-point transmission of object under test.

Its effect of the present invention is, though distortion error appears in the waffle slab image; Because object under test is in identical object plane with waffle slab, measurement mechanism is constant, therefore; When measuring the object under test size, its distortion in images error is identical with waffle slab pattern distortion error.So, because of whether p on the distortion grid plate takes place ₁, p ₂2 distances in waffle slab coordinate system image look different, and still, the distance in the waffle slab coordinate system is constant, sees shown in Figure 4.Be in A on the object under test on the identical object plane with waffle slab ₁, A ₂2 distances in the waffle slab coordinate system because of whether the waffle slab image distortion takes place do not change equally, and therefore, the present invention directly uses the waffle slab that distortion takes place to measure A on the object under test ₁, A ₂2 distances in the waffle slab coordinate system.No longer set up image coordinate system, also no longer pass through the correcting distorted error of setting up of mathematical model for demarcation.Especially for the irregular target surface dimensional measurement of distortion error, modeling is difficult to, and the present invention's method can be simply suitable.When the dimensional accuracy of waffle slab used in the present invention was 0.2 μ m, measuring accuracy was higher than 3 μ m.

Description of drawings

Fig. 1 is the waffle slab synoptic diagram in the waffle slab coordinate system.Fig. 2 is the waffle slab image synoptic diagram that distortion takes place in image coordinate system.Fig. 3 is the interval synoptic diagram of waffle slab image division that distortion takes place in image coordinate system.Fig. 4 is the waffle slab coordinate system synoptic diagram that distortion takes place.Fig. 5 is that the object under test point is positioned at the situation synoptic diagram outside the waffle slab grid that distortion takes place in search procedure single-frame.Fig. 6 is the situation synoptic diagram that the object under test point is positioned at the waffle slab grid that distortion takes place in search procedure single-frame.Fig. 7 is any 2 situation synoptic diagram that drop on respectively in the waffle slab grid that distortion takes place on the object under test.Fig. 8 is the interior object under test point exact position of the waffle slab grid synoptic diagram that distortion takes place, and this figure double as is a Figure of abstract.

Embodiment

At first, residing grid in the waffle slab of confirming after imaging, to take place to distort after any 2 imagings of object under test.This process is also referred to as preliminary survey.If certain grid on the waffle slab that takes place to distort is quadrilateral BCDE.The line of four summit B of any 1 A of object under test and quadrilateral BCDE, C, D, E forms four triangle △ BCA, △ CDA, △ DEA, △ EBA.When triangle △ BCA, △ CDA, △ DEA, △ EBA area sum during greater than quadrilateral BCDE area, see shown in Figure 5ly, decision-point A drops on outside this grid.Through single-frame search, as triangle △ BCA, △ CDA, △ DEA, when △ EBA area sum equals quadrilateral BCDE area, see shown in Figure 6ly, decision-point A drops in this grid.Confirm to belong to more in addition grid again.Thereby obtain this 2 A ₁, A ₂Coordinate in the waffle slab coordinate system is obtained the target surface size of this point-to-point transmission.As an object lesson, judge A ₁In (2,7) grid, A ₂In (6,3) grid,, obtain the preliminary survey target surface and be of a size of according to the distance between two points formula:

$L^{\′}=\sqrt{{(2d-6d)}^2+{(7d-3d)}^2}=5.657d---\left(8\right)$

D is the target surface size between the waffle slab any two adjacent cross centers in the formula.

Secondly, in said 2 residing grids, set up coordinate system respectively, obtain and the target surface size between coordinate origin separately at these 2.This process is also referred to as accurate measurement.The intrinsic coordinates value of certain grid on the waffle slab of confirming to take place after any 1 imaging that A was positioned on the object under test to distort.Preliminary survey confirms that it is among the quadrilateral BCDE that object under test point A drops on certain grid of waffle slab that distortion takes place, and the true origin of establishing quadrilateral BCDE coordinate system is the E point, and EB is the x axle, and ED is the y axle, establishes:

$p=\frac{\mathrm{EM}}{\mathrm{ED}}=\frac{n}{n+m}---\left(9\right)$

P just puts the ratio of y axial coordinate value with the y axial length of A.

Distortion error in the quadrilateral BCDE is regarded as even distribution, and according to the opposite side bisecting method, the M point coordinate is:

x _M＝(x _E-x _D)p (10)

y _M＝(y _E-y _D)p

In like manner, the N point coordinate is:

x _N＝(x _B-x _C)p (11)

y _N＝(y _B-y _C)p

Because certain some A is positioned on the straight line MN on the object under test, then has:

$\frac{x_A-x_M}{y_A-y_M}=\frac{x_A-x_N}{y_A-y_N}---\left(12\right)$

Formula (10), (11) substitution (12), obtain:

$p=\frac{x_A(y_B+y_D-y_C-y_E)+y_A(x_E+x_C-x_B-x_D)}{(y_E-y_D)(x_B-x_C)-(y_B-y_C)(x_E-x_D)}---\left(13\right)$

Combinatorial formula (9), (13) obtain:

n＝dp

m＝d(1-p)

In like manner, establish $q=\frac{\mathrm{EF}}{\mathrm{EB}}---\left(14\right)$

Q just puts the ratio of x axial coordinate value with the x axial length of A.Then can get:

EF＝dq (15)

Can access any 2 A of testee according to foregoing ₁, A ₂The intrinsic coordinates value of certain grid is respectively on the waffle slab that distortion takes place:

$\left\{\begin{array}{c}{x}_{A_1}={\mathrm{dp}}_1\\ y_{A_1}={\mathrm{dq}}_1\end{array}\right.---\left(16\right)$

$\left\{\begin{array}{c}{x}_{A_2}={\mathrm{dp}}_2\\ y_{A_2}={\mathrm{dq}}_2\end{array}\right.---\left(17\right)$

According to the distance between two points formula, obtain A ₁, A ₂2 with the distance of coordinate origin separately (target surface size) and be:

$L^{\′\′}=\sqrt{{\left({\mathrm{dp}}_1\right)}^2+{\left({\mathrm{dq}}_1\right)}^2}+\sqrt{{\left({\mathrm{dp}}_2\right)}^2+{\left({\mathrm{dq}}_2\right)}^2}$

That is: $L^{\&prime;\&prime;}=d(\sqrt{{{\mathrm{<figure-callout\; id="1"\; label="p"\; filenames="H2009102056301E00021.png"\; state="\{\{state\}\}">p</figure-callout>}}_1}^2+{{\mathrm{<figure-callout\; id="1"\; label="q"\; filenames="H2009102056301E00021.png"\; state="\{\{state\}\}">q</figure-callout>}}_1}^2}+\sqrt{{{\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="H2009102056301E00011.png,H2009102056301E00021.png"\; state="\{\{state\}\}">p</figure-callout>}}_2}^2+{{\mathrm{<figure-callout\; id="2"\; label="q"\; filenames="H2009102056301E00011.png,H2009102056301E00021.png"\; state="\{\{state\}\}">q</figure-callout>}}_2}^2})---\left(18\right)$

In the formula: d is the target surface size between the waffle slab any two adjacent cross centers, P ₁Be arbitrfary point A on the object under test ₁The ratio of y axial coordinate value and y axial length, P ₂Be another arbitrfary point A on the object under test ₂The ratio of y axial coordinate value and y axial length, q ₁Be arbitrfary point A on the object under test ₁The ratio of x axial coordinate value and x axial length, q ₂Be another arbitrfary point A on the object under test ₂The ratio of x axial coordinate value and x axial length.

The 3rd, the addition of preceding two resulting target surface sizes of step is obtained the target surface size of any point-to-point transmission of object under test.Connect the used object lesson of preliminary survey, combinatorial formula (8) and (18) obtain A ₁, A ₂Total target surface of 2 is of a size of:

$L=L^{\&prime;}+L^{\&prime;\&prime;}=5.657d+d(\sqrt{{\left(p_1\right)}^2+{\left(q_1\right)}^2}+\sqrt{{\left(p_2\right)}^2+{\left(q_2\right)}^2})---\left(19\right)$

Claims (3)

1. model-free method for correcting distortion error; It is characterized in that, at first, residing grid in the waffle slab of confirming after imaging, to take place to distort after any 2 imagings of object under test; Thereby obtain this 2 coordinates in the waffle slab coordinate system, obtain the target surface size between these 2 residing grids; Secondly, in the grid of said 2 residing generations distortion, set up coordinate system respectively, obtain and the target surface size between coordinate origin separately at these 2; The 3rd, the addition of preceding two resulting three target surface sizes of step is obtained the target surface size of any point-to-point transmission of object under test.

2. bearing calibration according to claim 1; It is characterized in that; If certain grid on the waffle slab that takes place to distort is quadrilateral BCDE; The line of four summit B of any 1 A of object under test and quadrilateral BCDE, C, D, E forms four triangle △ BCA, △ CDA, △ DEA, △ EBA, and when triangle △ BCA, △ CDA, △ DEA, △ EBA area sum during greater than quadrilateral BCDE area, decision-point A drops on outside this grid; Through single-frame search, as triangle △ BCA, △ CDA, △ DEA, when △ EBA area sum equals quadrilateral BCDE area, decision-point A drops in this grid; Confirm to belong to more in addition grid again.

3. bearing calibration according to claim 1 is characterized in that, any 2 A on the object under test ₁, A ₂And separately the target surface size between the coordinate origin and L " be:

$L^{\&prime;\&prime;}=d(\sqrt{{p_1}^2+{q_1}^2}+\sqrt{{p_2}^2+{q_2}^2}),$

In the formula: d is the target surface size between the waffle slab any two adjacent cross centers, P ₁Be arbitrfary point A on the object under test ₁The ratio of y axial coordinate value and y axial length, P ₂Be another arbitrfary point A on the object under test ₂The ratio of y axial coordinate value and y axial length, q ₁Be arbitrfary point A on the object under test ₁The ratio of x axial coordinate value and x axial length, q ₂Be another arbitrfary point A on the object under test ₂The ratio of x axial coordinate value and x axial length.

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